1. Field of the Invention
The present invention generally relates to a disc reproducing method and apparatus which utilize a disc motor for rotating a disc and an optical pickup to realize high speed reproduction, and more particularly relates to a disc reproducing method and apparatus which are suitable for prevention of excessive oscillation and/or vibration in a radial direction of a disc during high speed rotation resulting from an imbalance (e.g., disc eccentricity imbalance, mass imbalance, etc.).
2. Description of Related Art
Use of a so-called compact discxe2x80x94read only memory (CD-ROM) apparatus (utilizing CD-ROM""s as recording/reproduction medium) as a peripheral device of a personal computer has gained in popularity and frequency in recent years. Since introduction, whereupon the CD-ROM apparatus was standardized to operate at a predetermined 1xc3x97speed or rate, technology has advanced tremendously, leading to ever increasing operating speeds for the CD-ROM apparatus, i.e., for realization of higher speed data transfer rates. Recently, an 8xc3x97speed (i.e., 8 times the original standardized 1xc3x97speed) is commonplace, and it is now estimated that high speed data transfer of a 12xc3x97speed or higher will become commonplace in the near future.
For background discussion, FIG. 7 shows a schematic basic block diagram of a servo system used for disc motor control of a disc reproducing apparatus. More particularly, the FIG. 7 arrangement may be dedicated to reproduce only CD-ROMs on which the information of a computer (hereinafter called CD-ROM information) is recorded, or may also be able to reproduce CDs on which audio information is recorded. If the disc 1 is a CD, the rotational speed is uniquely defined, however, if the disc 1 is a CD-ROM, for example, it can be reproduced at a multiplicity of different speeds, e.g, X times as high as a standardized rotational speed of 1.2 m/sec. More particularly, as described above, recently reproduction at an 8xc3x97 or 12xc3x97rate is mainstream.
Within FIG. 7, the information reader 4 (i.e., head arrangement including a laser, lenses, sliders, actuators, etc.) converts information recorded on a disc 1 into an electrical signal and then inputs the signal to a demodulating circuit 6. The demodulating circuit 6 demodulates the electrical signal and a signal processing circuit 7 generates a clock signal from the demodulated signal. A disc motor servo circuit 8 controls the rotating speed of a disc motor 2 via the disc motor driving circuit 3 so that the clock signal becomes equal to a reference clock signal generated by a reference clock generating circuit 9.
FIG. 8 shows relationship between a disc reproducing rate multiplication ratio according to a reproducing position and a disc rotating speed. The recording/reproducing system of this exemplary CD-ROM is a constant linear velocity (CLV) system in which linear speed is set to a constant value. In this system, a rotating speed of the disc changes depending on a current reproducing position of the head on the disc. In such discussed CLV system, since a reference rotating speed is 1.2 m/sec in a standard reproducing rate (i.e., in a 1xc3x97original standard speed) and a signal recording area of a disc is within a disc region from 25 mm to 58 mm in a radius direction from a center of the disc, for a 4xc3x97 (i.e., 4-fold) reproducing operation, the rotating speed (frequency) at an innermost position of the 25 mm radius is about 32 Hz as can be seen from the characteristic curve 30 in FIG. 8. Similarly, in an 8xc3x97 (i.e., 8-fold) reproducing operation, the maximum rotating speed is about 64 Hz as can be seen from the characteristic curve 31, and in the 12xc3x97 (i.e., 12-fold) reproducing operation, the maximum rotating speed is about 96 Hz as can be seen from the characteristic curve 32.
Turning discussion now to FIG. 9, at times, a certain disc 1 which is loaded into and attempted to be reproduced (i.e., read) by a disc reproducing apparatus may have a center of rotation 33 (which is the center of disc 1) which is deviated from a center of gravity or center of mass point 34. Such disc situation is hereinafter called a deviated gravity disc. Such deviated gravity disc may be generated during manufacturing, for example, because a disc material pressure is uneven, an unbalanced paint distribution is applied to a surface of the disc, or by reason that an index label is attached on the disc surface after manufacturing thereby to imbalance the disc. When this deviated gravity disc 1 is rotated around the center 33, a force indicated by a force vector 35 is generated at the point 33, in a direction of the point 34. Therefore, when this deviated gravity disc 1 is reproduced by the disc reproducing apparatus, the force 35 works on the disc, disc clamp/mount and disc motor during rotation to fling the disc side to side, and vibration may be generated in a direction matching a major plane of the disc reproducing apparatus. Such situation is called a mass eccentric disc.
The above-mentioned force 35 increases in proportion to a square of the disc rotating speed. Namely, during a reproducing operation in the 8xc3x97reproducing rate, a force equal to 4 times that in the 4xc3x97reproducing rate is generated, and during a reproducing operation in the 12xc3x97reproducing rate, a force equal to 9 times that of the 4xc3x97reproducing rate is generated. Therefore, with improvement in a disc reproducing rate (i.e., rotating speed) of the disc reproducing apparatus, vibration generated when a deviated gravity disc is reproduced becomes large. Such vibration can result in a failure of operation (e.g., burn out, mis-reading, etc.) of the disc reproducing apparatus, can have an adverse effect on components installed in close proximity to the vibrating disc, a noise generated therefrom can be an annoyance to a user, and/or vibration can cause the disc reproducing apparatus to move across a surface on which it is placed.
The above-discussed vibration phenomenon is due to a mass eccentricity imbalance of the disc, causable (i.e., presently causing or capable of causing) of at least one of a radial oscillation and radial vibration above a predetermined rotational speed, i.e., oscillation/vibration directed along a radial direction (i.e., in a major plane) of the disc so as to cause a disc to fling side-to-side as the disc is rotated. Such mass eccentricity imbalance is the imbalance of most interest in the present invention. Another imbalance of interest to a smaller degree is a centering eccentricity imbalance, i.e., a centering eccentricity imbalance of the disc, causable of at least one of a radial oscillation and radial vibration above a predetermined rotational speed, i.e., oscillation/vibration directed along a radial direction (i.e., in a major plane) of the disc so as to cause a disc to fling side-to-side as the disc is rotated. Centering eccentricity imbalance results, for example, when a disc is loaded with its disc center misaligned to a center of a rotator arrangement (i.e., rotating motor, disc mount/clamp, etc.). Misalignment may be due to sloppy loading of the disc to the mount/clamp, excessively sized central mounting hole in the disc, excessively small or worn mount/clamp, etc. Centering eccentricity imbalance affects oscillation/vibration and operation of the disc reproducing apparatus to a lesser degree than that of mass eccentricity imbalance. However, the principles and arrangements of the present invention are equally applicable to centering eccentricity imbalance as mass eccentricity imbalance.
Continuing in discussion, FIG. 14 is a block diagram showing another CD/CD-ROM disc reproducer arrangement, and in greater detail. More particularly, a reference number 1 denotes a disc, T denotes a track or tracks, L denotes a beam (e.g., laser beam), 2 denotes a disc motor, 3 denotes a disc motor driver or control circuit, 4 denotes a head arrangement or information reader, 40 denotes a preamplifier circuit, 5 denotes a tracking driver or control circuit, 7 denotes a signal processing circuit, 50 denotes a CPU, 10 denotes an audio circuit, 11 denotes an audio signal output terminal, 12 denotes a CD-ROM decoder and 13 denotes a CD-ROM signal output terminal. More particularly, the FIG. 14 arrangement can be used to reproduce both CDs and CD-ROMs as was discussed above with respect to the arrangement of FIG. 7. CPU 50 receives a request along an input line 1 from an external device such as a host computer, issues an instruction A for rotational speed to a disc motor control circuit 3 in response to this request, and sets the rotational speed of the disc 1 to a speed requested from the external device.
Helical or concentric tracks T where information is recorded are formed on the disc 1, and an information reader 4 reads audio information or CD-ROM information from any selected track T by radiating a beam L (e.g., a laser beam) on this track T and outputs reflected read information as a read signal. After this read signal is amplified and the waveform is shaped by a preamplifier circuit 40, the signal is supplied to a signal processing circuit 7, and predetermined processing is applied to the signal. More particularly, if the read signal is an audio information signal, the signal is further processed in an audio circuit 10, or if the read signal is a CD-ROM information signal, it is processed in a CD ROM decoder 12, and output from output terminals 11 and 13, respectively.
The head arrangement or information reader 4 may be constituted by laser, lenses, a pickup, a main actuator/slider for coarsely moving the pickup for major distances (i.e., across tracks) in the radial direction of the disc 1, a minor actuator/slider for finely moving the pickup for minor distances (i.e., precisely aligning to a particular track) in the radial direction of the disc 1, a focusing actuator/slider for focusing the laser beam L onto a track surface of the disc, and may have additional components. A beam L from the pickup can sequentially radiate a series of tracks T owing to movement of the actuators/sliders as the disc 1 is rotated. The disc reproducer is further provided with a tracking control circuit 5 for controlling a position of this condenser in the direction of the width of the track T so as to let a beam L follow the track T, and other components. A part of a read signal amplified by the preamplifier circuit 40 is supplied to a tracking driver or control circuit 5. This tracking control circuit 5 detects a state in which a beam L is following the track T based upon the supplied read signal and generates a tracking control signal B according to the result of detection. The tracking control of the pickup of the information reader 4 is controlled by this tracking control signal B so that a beam L always precisely follows the track T.
To access a desired track T, CPU 50 outputs an inhibiting signal C to stop the operation of the tracking control circuit 5 so that a tracking control signal B is prevented from being output and moves the pickup of the information reader 4 in the radial direction of the disc 1 at high speed by the slider so that a beam L is radiated upon this desired track T. This allows a beam L to cross plural tracks causing a read signal outputted from the information reader 4 to be a pulse signal having an amplitude which fluctuates or pulses every time the beam L crosses a track, which pulse signal is called a track crossing pulse hereafter. The track crossing pulse D is detected by and supplied from the preamplifier circuit 40 to CPU 50. CPU 50 recognizes the number of tracks which the beam L crosses by counting a number of track crossing pulses D and determines whether a beam L has reached a desired track or not.
When the tracking control circuit 5 supplies a tracking control signal B to the information reader 4, the tracking control arrangement is controlled and a beam L follows the track T with the pickup theoretically stopped opposing a desired track in this information reader 4. However, in practice stopping the pickup opposed to a desired track may not be practical because a track location may oscillate (due to eccentricity as described above and below) and because there is a limit in the quantity of displacement (fine adjustment) of a beam L by the tracking arrangement. Accordingly, in a practical situation, the pickup is typically adjustingly moved in the radial direction of the disc by the actuators/sliders and tracking arrangement periodically, i.e., the pickup is intermittently moved in the radial direction of the disc 1.
If such a mass eccentric disc is rotated at a low rotational speed, for example, a 1xc3x97speed, oscillation may hardly occur because rotational speed is slow. However, when rotational speed is increased to a high rotational speed, for example 8xc3x97 or 12xc3x97 (in order to accomplish high speed reproduction), the disc reproducer may experience oscillation/vibration and track eccentricity in a direction parallel to a major plane of the disc. More particularly, oscillation/vibration and track eccentricity may be only experienced or increased as rotational speed is increased. For track eccentricity below a predetermined value, tracking control and track following can still be accomplished, but if above the predetermined value, tracking control and track following cannot be accomplished. Though it varies depending upon the quantity of mass eccentricity, according to experiments, when reproduction is executed at approximately a 6xc3x97rate or more, oscillation/vibration, track eccentricity and noise occurs. Therefore, in the case of reproduction of a mass eccentric disc at an 8xc3x97rate which is the recent mainstream, a large oscillation/vibration, track eccentricity and noise are generated by the disc reproducer, undesirable oscillation may be applied to components installed in close proximity to the disc, and such oscillation may have a detrimental effect upon components of and work around this disc reproducer.
As an example of a detrimental effect on a particular component, in a pickup, a condenser is normally held by an elastic member and the position of this condenser is controlled according to a tracking control signal supplied to tracking arrangement so that a beam follows (that is, tracks) a track. However, when this tracking control is stopped, the condenser held by the elastic member is oscillated by and in synchronization with the disc imbalance vibration. When a disc reproducer is oscillated by the rotation of a mass eccentric disc at low rotational speeds, the free condenser is oscillated slightly at the same phase as this disc reproducer because the disc oscillation is small. However, when the rotational speed of the disc is increased, the amplitude/frequency of oscillation generated in the disc reproducer is increased, and the condenser is oscillated at a frequency according to the transfer function proper to the elastic member holding the condenser.
This invention is directed toward satisfying the aforementioned imbalance and oscillation/vibration problems in reproduction of a disc. More particularly, it is an object of the present invention to provide a disc reproducing method and apparatus which assure higher reliability and safety in operation by preventing an excessive oscillation/vibration generated during rotation of an imbalanced disc.
As explained above, when an imbalanced disc is rotated/reproduced at high reproduction rates (e.g., 8xc3x97, 12xc3x97), vibration becomes large. In order to combat such problem, when an imbalance vibration is generated and encountered during high speed reproduction at a predetermined rotational speed, vibration can be lowered by reducing and/or increasing the rotational speed (i.e., reproduction rate). More particularly, a lowering of rotational speed substantially lowers an imbalance force (vector 35; FIG. 9), thereby to eliminate the generation of vibration. In contrast, a raising of rotational speed will eventually reach a situation where a mass of the disc, disc/clamp, motor shaft, etc. is too great to move fast enough to follow the high rotational frequency of the imbalance force (vector 35; FIG. 9), thereby avoiding vibration.
Moreover, in order to attain the objects explained above, according to the disc reproducing method of the present invention, information indicating an imbalance (e.g., deviated gravity, eccentricity) of the disc is detected and when smaller than a predetermined value, a disc reproducing operation is performed at a first reproducing rate, and when larger, the disc reproducing operation is performed at a second reproducing rate which is lower than the first reproducing rate.
Therefore, in view of achieving the objects explained above, according to one disc reproducing method and apparatus of the present invention, information about vibration of the disc reproducing apparatus is detected, and when such information indicates a level of vibration smaller than a predetermined value, disc reproducing operation is performed at a normal reproducing rate, and when such information indicates vibration larger than the predetermined value, a disc reproducing operation is performed at a substitute reproducing rate which is different (i.e., lowered or raised) from the normal reproducing rate.
In addition, the disc reproducing apparatus of the present invention comprises, in view of achieving the object explained above, a switching controller for controlling the switching of the disc reproducing rate to the first reproducing rate or the second reproducing rate (i.e., higher or lower second reproducing rate), so as to control the disc reproducing rate to the first reproducing rate when a detected signal from the vibration information detector is smaller than the predetermined value, and to the second reproducing rate when the detected signal is larger than the predetermined value.
Moreover, the disc reproducing apparatus of the present invention further can comprise, in order to achieve the object explained above, a deviated gravity information detector for detecting information about a deviated gravity of a disc, and a switching controller for controlling switching of the disc reproducing rate to the first reproducing rate or to second reproducing rate which is lower than the first reproducing rate, i.e., to set the disc reproducing rate to the first reproducing rate when the detected signal from the deviated gravity information detector is smaller than the predetermined value and to the second reproducing rate when the detected signal is larger than the predetermined value.
In addition, the present invention also comprises a display so that a user can confirm a present state of the arrangement, i.e., as to whether or not an imbalanced condition has been detected, and/or as to whether or not the disc reproducing rate is switched to the second reproducing rate from the first reproducing rate.
Construction according to the present invention enables high speed reproduction, for example, of a 12xc3x97 (i.e., 12-fold) rate when gravity deviation of disc is judged to be small or when vibration is sufficiently small so as not to represent any problem even under a high reproduction rate, and also enables automatic switching of the disc reproducing rate to an appropriate changed rate depending on a degree of gravity deviation or vibration. More particularly, automatic switching can be provided to switch from a normal desirable 12xc3x97speed to a differing (i.e., lower or higher) speed, for example, an 8xc3x97speed or 4xc3x97speed under control by the switching controller when gravity deviation of disc is judged to be large or when vibration is generated under a present reproduction rate.
Alternative to dynamic detection, a static detection arrangement can be used wherein the quantity of mass eccentricity of a disc which is equivalent to the quantity of displacement between the center of gravity of the disc and the center point of the disc is detected beforehand to automatically warn or inhibit reproduction of the mass eccentric disc at high speed.
In accomplishing the above objects, however, provision of required detectors for detecting the oscillation of a disc reproducer, for detecting the quantity of mass eccentricity of a disc and others do not have to be provided by additional components added to a disc reproducer, i.e., the number of parts, scale and cost of circuits/arrangements of a disc reproducer do not have to be increased as the present invention can be implemented with components already present in disc reproducing apparatus. More particularly, another specific object of the present invention is to provide a mass eccentric disc detecting method which enables detecting the quantity of mass eccentricity of a disc precisely without or only minimally adding equipment to a disc reproducer arrangement.
A further object is to provide a disc reproducer which can provide automatic control so that if the disc is a mass eccentric disc, the rotational speed of the disc is made optimum according to a quantity of mass eccentricity.
To achieve the above object, according to the present invention, a disc is rotated at first rotational speed and at second rotational speed which is faster than the first rotational speed with tracking control stopped, a track crossing signal which is a pulse every time a beam crosses a track on a disc is obtained at differing rotational speeds and the information of the quantity of mass eccentricity of a disc is detected based upon a comparison of track crossing counts at first and second rotational speeds.
As force generating oscillation due to the rotation of a mass eccentric disc is in proportion to the square of the rotational speed of this disc and the quantity of mass eccentricity of the disc, the oscillation of a disc reproducer is increased in proportion to the rotational speed of the disc, and if the above first rotational speed is slow rotational speed to the extent that the disc reproducer is hardly oscillated and the above second rotational speed is high rotational speed at which the disc reproducer is oscillated when a mass eccentric disc is rotated at the rate, in the case of the former the scanning trace of a beam on the disc forms substantially circular trace 90 shown by a dotted line in FIG. 15, however, in the case of the latter, when the condenser is oscillated at the frequency proper to the elastic member holding the condenser, for example the scanning trace forms oval trace 92 shown by a broken line in FIG. 15 because tracking control is not executed and the condenser is free.
If the circular trace 90 and the oval trace 92 are compared, in the case of the former the trace 90 is substantially along a track T because the track T is helical or circular and in the case of the latter, more tracks are crossed, a read signal obtained from a pickup is a pulse signal the frequency of which is high or the shortest cycle of which is short. Therefore, information showing the degree of the mass eccentricity of a disc can be obtained based upon the difference between both described above.
For a concrete method of detecting the information of the quantity of mass eccentricity of a disc according to the present invention, the number of the above pulse signals, that is, track crossing signals at the predetermined number of revolutions is counted or the cycle of this track crossing signal is detected and the above number of pulses, the ratio or the difference of a cycle at the above first and second rotational speed are obtained. The ratio or difference shows the degree of mass eccentricity of a disc.
According to the present invention, it is determined whether the disc is a mass eccentric disc or not based upon the quantity of mass eccentricity detected as described above and the allowable maximum rotational speed of a disc is limited according to the detected quantity of mass eccentricity. Hereby, in a disc reproducer, oscillation can be prevented from being caused.
Further, according to the present invention, the information of the detected quantity of mass eccentricity is displayed on display to let the outside know whether an installed disc is a mass eccentric disc or not.